1. Technical Field
This invention relates to a data processing system such as a personal computer. In particular, the invention relates to an information processing system including multiple read-only memory (ROM) images each storing a basic input output system (BIOS) program for executing initialization and so forth during a boot.
2. Description of the Related Art
A BIOS program generally includes a BIOS main body (core block) for executing initialization of various types of devices, loading of an operating system (OS), and so forth and a boot block that boots up immediately after a computer is turned on or reset to execute a cyclic redundancy check (CRC) or the like to detect an error and returns control to the BIOS main body if there is no problem. The BIOS program's failure in operating normally prevents the computer from booting up, so some configurations have been adopted to cope with such failure.
In general, a central processing unit (CPU) reads and executes an instruction from an address set up in a program counter. When the power is turned on, the program counter is set to a default, which typically refers to the top of an initialization code in a ROM. Incidentally, writable flash ROMs have often been used as ROMs in recent years. This is advantageous in that a flash memory can be rewritten without having it to be removed even if a problem has occurred in a program.
Corruption or erasure of an initialization code per se in a flash ROM prevents the system from booting up. Therefore, the initialization code is handled in a special manner as a boot block in the flash ROM, and its rewriting is restrained as much as possible. For this reason, the initialization code stored in the boot block is generally programmed so as to be processed independently of a function block. Upon completing initialization of the system, the initialization code transfers control to the function block and the system performs ordinary processes.
FIGS. 12(a) and 12(b) each show an example of a flash ROM including a boot block. A boot block is typically disposed from a memory address of 0 and a function block is disposed in a subsequent address. This disposition may vary depending on the type of a CPU used in an information processing (computer) system. The examples shown in FIGS. 12(a) and 12(b) each have only one boot block. On the other hand, the example shown in FIG. 12(a) has one function block and the example shown in FIG. 12(b) has two function blocks. If there are multiple function blocks, for example, two function blocks as shown in FIG. 12(b), a function block 1 includes a new function code and a function block 2 includes the preceding function code. The older function code in the function block 2 is rewritten at the subsequent rewriting.